U.S. Pat. No. 4,406,899, issued Sept. 27, 1983 to Aburaki et al., discloses compounds of the formulae ##STR1## wherein Ph is phenyl, and ##STR2## or an N-silyl derivative thereof, wherein B.sup.1 is hydrogen or a conventional carboxyl-protecting group. These compounds are not exemplified in the patent, but are disclosed by structural formulae only, as intermediates in an alternate reaction scheme for the preparation of certain cephalosporins (by acylation and then deblocking of the protected carboxyl group). The reaction scheme actually exemplified did not utilize these compounds (and also required deblocking of the protected carboxyl group as the final step). Each of the final products of U.S. Pat. No. 4,406,899 required a chromatographic purification step to separate the mixture of .DELTA..sup.2 and .DELTA..sup.3 isomers which were produced.
U.S. Pat. No. 4,168,309, issued Sept. 18, 1979 to Barry E. Ayres, discloses compounds of the formula ##STR3## wherein R"' is a carboxyl-protecting group; R.sup.1, taken together with the carbon atom to which it is attached, forms an optionally substituted saturated or partially saturated 4-10 membered heterocyclic ring which may contain one or more further heteroatoms selected from O, N and S; the dotted line indicating a ceph-2-em or a ceph-3-em compound; and X.sup..crclbar. representing an anion; and acid addition salts or an N-silylated derivative thereof.
These compounds are not exemplified but are disclosed by structural formula only as intermediates in an alternative synthesis of certain cephalosporins (by acylation and then deblocking of the protected carboxyl group). The reaction scheme actually exemplified did not utilize these compounds (and also required deblocking of the protected carboxyl group as a final step).
The use of blocked carboxyl groups in the processes of the above two patents has the disadvantage of requiring deblocking after acylating whereby acyl group is lost in the deblocking step due to less than 100% yield in the deblocking step.